1. Field of the Invention
The present invention relates to a method for manufacturing a core of a motor for washing machines, in which a core band is made of an electric steel plate by punching, and then spirally wound, and then securing parts are welded to an inner cylindrical surface of the wound core band.
2. Description of the Related Art
FIG. 1 is a cross-sectional view of a conventional motor for washing machines.
Generally, a motor for washing machines comprises a housing 2, a stator 10, a rotor 20, and a rotary axis 4. The housing 2 is secured to an outer cylindrical surface of a washing tub (not shown) for washing and spin-drying the laundry. The stator 10 is bolted to the housing 2. The rotor 20 is disposed at the outside of the stator 10 and rotated interactively with the stator 10. The rotary axis 4 is configured so that one end of the rotary axis 4 is rotatably connected to the rotor 20, and the other end of the rotary axis 4 is rotatably connected to a moving vane (not shown) contained within the washing tub.
The stator 10 comprises a core 12 including a ring-shaped yoke 12b and a plurality of teeth 12a regularly spaced on the yoke 12b, and a coil (not shown) wound on the teeth 12a of the core 12 and connected to an external power source. The teeth 12a are formed on the yoke 12b along its circumference and spaced from each other by slots (not shown) formed therebetween. Thus, the stator 10 serves as an armature for generating a rotating magnetic field when current flows into the coil.
Herein, a boss part 16 is protruded from an inner cylindrical surface of the yoke 12b and includes first bolt holes 16a. Since second bolt holes 2a are formed on the housing 2 so as to correspond to the first bolt holes 16a, bolts 6 are inserted into the corresponding first and second bolt holes 16a and 2a and nuts 8 are coupled with ends of the corresponding bolts 6 protruding from the first and second bolt holes 16a and 2a, thereby securing the stator 10 to the housing 2.
The rotor 20 comprises a cuplike rotor frame 22 and a plurality of magnets 24. The rotor frame 22 surrounds the circumference of the stator 10, and one end of the rotary axis 4 is secured to the center of the rotor frame 22. The magnets 24 are fixed to the inner cylindrical surface of the rotor frame 22 so as to be opposite to the stator 10, and operated interactively with the stator 10.
Non-described reference numeral 18a and 18b denote insulators.
When current supplied from the external power source flows into the coil in the above-described motor for washing machines, a magnetic torque is generated between the stator 10 and the magnets 24 and the rotor 20 is rotated in a designated direction so as to minimize its reluctance. As the rotary axis 4 is rotated together with the rotation of the rotor 20, the rotary axis 4 causes the moving vane or an inner tub of the washing tub to rotate, thereby achieving washing and spin-drying functions.
FIG. 2 is a schematic view illustrating a process for manufacturing the core of the conventional motor for washing machines, and FIG. 3 is a flow chart showing the process for manufacturing the core of the conventional motor for washing machines.
The process for manufacturing the core of the conventional motor for washing machines is described as follows.
First, sectional cores 12′, each having a sector shape obtained by dividing the ring-shaped core 12 into six equal parts, are formed out of an electric steel plate 25 by punching. A sectional core assembly 12″ is formed by stacking a plurality of the sectional cores 12′ to a designated height (h). Then, six sectional core assemblies 12″ are interconnected in a circumferential direction, thereby completely forming a ring-shaped core 12.
Herein, a recess (a) with a designated shape is formed on one end of a sectional yoke 12b′ of the sectional core 12′ and a protrusion (b) with a shape complementary with the recess is formed on the other end of the sectional yoke 12b′ in the circumferential direction. Therefore, when the sectional core assemblies 12″ are interconnected in the circumferential direction so as to form one ring-shaped core 12, the protrusion (b) of one sectional core 12′ is inserted into the recess (a) of the neighboring sectional core 12′. Thereby, the sectional core assemblies 12″ are electrically and magnetically interconnected.
Interconnecting parts between the sectional core assemblies 12″ in the core 12 are welded at the inner cylindrical surface of the core 12. Then, the sectional core assemblies 12″ are integrated as one complete ring-shaped core 12.
A pair of insulators 18a and 18b are individually inserted into the upper and lower surfaces of the completed core 12 so as to insulate the core 12 from the exterior, and a coil 14 is wound on each of the teeth 12a of the core 12 a predetermined number of times. Thereby, the stator 10 is completed.
Non-described reference numeral 12c denotes slots of the core 12, and non-described reference numerals 16 and 16a denote the boss part and the first bolt holes as shown in FIG. 1.
In the process for manufacturing the conventional core 12 of the motor for washing machines, after the sectional core 12′ is formed of the electric steel plate 25 by punching, a part 25′ of the electric steel plate 25 comprising 55˜60% of the total size of the electric steel plate 25 remains unused. Thus, the electric steel plate 25 is wastefully consumed.
Further, the protrusion (b) of the sectional core 12′ must be inserted into the recess (a) of the neighboring sectional core 12′ and the interconnecting parts between the sectional core 12′ must be welded, when the sectional core assemblies 12″ are interconnected in the circumferential direction. As a result, the manufacturing process is complicated.
Moreover, since the core 12 comprises a plurality of the sectional core assemblies 12″ formed by stacking the sectional cores 12′, and the sectional core assemblies 12″ of the core 12 are easily dislocated vertically at the welded parts, the core 12 has a poor degree of strength, thereby increasing vibration and noise in a high-speed spin-drying mode of the washing machine.